The present invention relates to a clutch transmission, in particular a dual-clutch transmission for a vehicle, in particular a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Dual-clutch transmissions are preferably used in passenger automobiles. A dual-clutch transmission usually includes two coaxially arranged gear input shafts which are each associated with a respective transmission, to be referred here also as subsidiary transmissions. A corresponding clutch is associated with each of the gear input shafts, which can be used to frictionally couple via the gear input shafts of the respective transmission the gear input shaft with the output of a motor, preferably a combustion engine of a motor vehicle. A first of the two transmissions typically includes the odd gears, whereas a second of the subsidiary transmissions includes the even gears and the reverse gear. Simple clutch transmissions typically include only a single clutch and only a single transmission which can be used to switch all gears of the clutch transmission.
Typically, one of the transmissions is active when driving, meaning that the gear input shaft associated with this transmission is coupled with the motor via the associated clutch. A gear is engaged in the active transmission which provides a current gear ratio. A controller determines if the next higher or next lower gear is to be engaged depending on the driving situation. This gear which may be used as the next gear is then engaged in the second inactive transmission. To change gears, the clutch of the inactive transmission is engaged, whereas the clutch of the active transmission is disengaged. Preferably, disengaging the clutch of the active gear and engaging the clutch of the inactive gear overlap each other such that the force flow from the motor to the drive shaft of the motor vehicle is not interrupted at all or is only slightly interrupted. Subsequent to the gear change, the previously active transmission becomes inactive, whereas the previously inactive transmission becomes the active transmission. Thereafter, the next potentially required gear can now be engaged in the now inactive subsidiary transmission.
The gears are engaged and disengaged by way of elements, preferably by way of selector rails, which are operated by hydraulic cylinders, the so-called switching cylinders already mentioned above. The hydraulic cylinders are preferably constructed as double-acting hydraulic cylinders, in particular synchronous cylinders or differential cylinders, so that two gears can preferably be associated with each switching cylinder. Alternatively, single-acting hydraulic cylinders may also be provided. The hydraulic cylinders operating the elements, in particular the selector rails, are also referred to as gear selector cylinders. A gear selector cylinder constructed as a synchronous cylinder having two associated gears has preferably three switching positions, wherein a predetermined gear is engaged in a first switching position, another predetermined gear in a second switching position, and none of the two aforementioned gears in a third switching position.
The clutches associated with the two transmissions are also hydraulically operated, meaning engaged or disengaged. Preferably, the clutch is engaged when hydraulic pressure is applied, whereas the clutch is disengaged when hydraulic pressure is not applied, i.e., pressure is relieved from a hydraulic cylinder—previously also referred to as coupling cylinder—associated with the respective clutch.
As already mentioned, clutch transmissions are controlled or regulated as well as cooled by a hydraulic circuit. The operation of a dual-clutch transmission is also known in the art and will therefore not be described here in greater detail.
In addition, vehicle transmissions are known with a so-called parking lock which locks the transmission when suitably actuated and thus particularly blocks the driven wheels of the vehicle. The parking lock can typically be operated with an electric motor or hydraulically.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved dual-clutch transmission with increased efficiency and functionality of the hydraulic circuit, which is inexpensive to manufacture and has a small number of individual components.